1. Field of the Invention
The present disclosure relates to component measurement apparatuses. A particular aspect of the present disclosure relates to improvement of a component measurement apparatus that measures concentrations and so forth of components using laser light.
2. Description of the Related Art
To date, in order to measure a concentration of a component such as a blood glucose level, in many cases human blood is collected with a syringe or by pricking a finger tip or an earlobe in order to measure a blood glucose concentration or so forth.
In general, a blood glucose level significantly changes depending on measurement conditions such as whether a subject has recently had a meal or not, or whether a subject performs exercise or not just before the blood sample is collected. Thus, frequent measurement is required in order to obtain correct blood glucose data. However, with a related art method in which a direct analysis is performed on a human blood sample that is collected every time such an analysis is performed, there is a problem in that the subject experiences a significant physical pain.
The assignee previously filed a patent application for a living body component measurement apparatus using a confocal optical system (see Japanese Unexamined Patent Application Publication No. 2008-301944). With this apparatus, a living body is illuminated by laser light, and the reflected light from the living body is detected. In accordance with a degree of laser light absorption by the living body (absorbance), the apparatus measures a concentration or so forth of a target component (for example, glucose in blood) without an invasive procedure for collecting a blood sample performed in the related art method.
FIG. 10 is a block diagram illustrating the living body component measurement apparatus disclosed in the above document. In FIG. 10, laser light emitted from a laser diode 1 is shaped into collimated light by a collimating lens 2 and strikes a half mirror 3 that is disposed so as to be inclined at about 45 degrees relative to the optical axis of the collimating lens 2. The laser diode 1 used here is, for example, a variable wavelength laser that can emit laser light in a wavelength region of 1600 nm to 1700 nm. Glucose absorbs a comparatively large amount of light in that wavelength region.
The collimated light having been transmitted through the half mirror 3 is condensed by an objective lens 4 and illuminates internal tissue of the living body LB. The laser light reflected by the internal tissue of the living body LB again strikes the objective lens 4, is shaped into collimated right, strikes the half mirror 3, and is redirected so as to be reflected at an angle of about 90 degrees.
The laser light, which has been reflected and redirected by the half mirror 3, is condensed by a lens 5 and strikes a pin hole 6. The laser light having passed through the pin hole 6 strikes a light-receiving element 7 and is converted into an electrical signal.
The light-receiving element 7 converts the received laser light into an electrical signal, the strength and the magnitude of which increase or decrease in accordance with the light amount of the received laser light, and sends the resultant signal to an analog to digital (A/D) converter 8. The A/D converter 8 converts the electrical signal received from the light-receiving element 7 into digital data, and sends the digital data to a data analyzer section 9.
When the living body LB is illuminated with laser light beams having two or more wavelengths different from each other, the data analyzer section 9 performs a quantitative analysis of a component of the living body LB in accordance with a plurality of electrical signals having been converted by and output from the light-receiving element 7.
Specifically, in order to quantitatively determine a blood glucose level, that is, a concentration of glucose in blood, a calibration curve that relates glucose concentrations having been measured to laser light absorbance values has been memorized in the data analyzer section 9 in advance. The data analyzer section 9 quantitatively determines a concentration of blood glucose of the living body LB in accordance with the calibration curve.
However, in the above-described related art living body component measurement apparatus, laser light emitted from the laser diode 1 is shaped into collimated light by the collimating lens 2 before the light strikes a half mirror 3. The laser light having been transmitted through the half mirror 3 is condensed by an objective lens 4 and illuminates internal tissue of the living body LB. As a result, there is a problem in that the living body component measurement apparatus needs considerable work time for assembly and adjustment such as alignment of the optical axes among optical components.